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In automatic transmissions, an open torque converter transmits torque from the engine to the transmission using fluid coupling. Although torque converters are ideal launch devices for automatic transmissions, they are inefficient in steady-state operations. An electronically controlled capacity clutch (ECCC) is implemented to control the slip between the pump and turbine of the torque converter, thereby increasing its energy transfer efficiency and increasing vehicle fuel economy. Even though reducing torque converter slip minimizes losses due to fluid coupling, it also decreases the damping provided by a slipping torque converter and as a result increases the sensitivity of the driveline to engine excitations. This investigation uses driveline torsional velocity response measurements to evaluate the effects of using slip feedback closed-loop control with a very aggressive torque converter ECCC slip schedule in automatic transmissions.

To realize better fuel economy benefits from transmissions, car makers have started the application of torque converter clutch control in second gear and beyond, resulting in greater demand on the torque converter clutch (TCC) and its control system. This paper focuses on one aspect of the control of the torque converter clutch to improve fuel economy and faster response of the transmission. A TCC is implemented to control the slip between the pump and turbine of the torque converter, thereby increasing its energy transfer efficiency and increasing vehicle fuel economy. However, due to the non-linear nature of the torque converter fluid coupling, the slip feedback control has to be very active to handle different driver inputs and road-load conditions, such as different desired slip levels, changes in engine input torques, etc. This non-linearity requires intense calibration efforts to precisely control the clutch slip in all the scenarios.